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What MOD or DP are your gears, I've generally found it better to do them in one pass unless very large teeth rather than several which just blunts the tips more, at the most take out the majority with one pass and then a light finish pass.
I've cut a fair few 32DP and MOD1 (25.4DP) on my X3 with single passes so your Tormach should be upto it, I would be happy doing that size on the KX3 CNC in one pass. The MOD1 cutters being the cheap far eastern ones are 50mm dia so can be run a little faster rpm wise but teh 32DP are the same dia as yours.
Estimate the cut area in CAD and do some math to find the cut torque. Does Tormach provide a tq/power curve for the spindle? When I had the Emco Mill 125 1HP I calculated cuts I thought would run into the torque or power limits. It really save a lot of headaches.
Power reduction below rated frequency is a characteristic of the motor, not the VFD.....